1. Field of the Invention
The invention relates in general to an input/output (IO) circuit with high voltage tolerance and associated apparatus, and more particularly to an IO circuit with high voltage tolerance and associated apparatus that avoids external high voltage by a clamping voltage provided by an internal switch circuit and a charge pump.
2. Description of the Related Art
Electronic devices are the most crucial hardware foundation of the modern information society. In an electronic device, multiple integrated circuits of different functions are disposed on a printed circuit, which facilitates signal transfer between the integrated circuits to accomplish overall function. To achieve such overall function, there is a need that different integrated circuits transfer data signals without interfering one another.
Certain integrated circuits, by being operated at a lower operating voltage and correspondingly having lower power consumption as well as operating temperature to meet power saving purposes, are extensively applied in various electronic devices. However, conventional low-voltage integrated circuits are also compromised by a lower voltage tolerance. During signal transfer between a low-voltage integrated circuit and a high-voltage integrated circuit via a printed circuit, in addition to noises and surges induced by the printed circuit, the low-voltage integrated circuit is prone to damages resulted from the relatively higher voltage of the high-voltage integrated circuit. For example, suppose an integrated circuit operates at 2.5V. During signal transfer between the 2.5V integrated circuit and another integrated circuit operating at 3.3V, the normal signal voltage of the 3.3V integrated reaches as high as 3.3V while noises of the printed circuit may be 0.3V to result an accumulated voltage of 3.6V, which exceeds the tolerable voltage of the 2.5V integrated circuit, such that the 2.5V integrated circuit malfunctions or even becomes damaged due to the external high voltage.
When the high-voltage integrated circuit is directly coupled to the low-voltage integrated circuit, signal errors and even more severe circuit damage may be incurred, and so a level shifter is interfaced between the two integrated circuits. However, the level shifter adds not only extra cost in hardware and assembly but also power consumption.